1. Field of the Invention
The present invention is generally related to nuclear reactors and more particularly to high temperature gas cooled reactors and their fuel elements.
2. General Background
In high temperature gas cooled reactors, forms of fuel that have been used include pin type fuel elements, cylindrical particle compacts in hexagonal graphite blocks (prismatic), spherical particle compacts (pebble), and extruded, hexagonal, graphite/fuel rods (NERVA). Reactors using the prismatic or pebble fuel forms utilize carbon as the matrix material binding coated fuel particles together and as the reactor moderator. Use of carbon as the moderator results in fuel elements with limited fuel particle content and very large reactor cores because of the large amount of carbon needed for neutron moderation. Patents directed to fuel elements for gas cooled reactors which applicant is aware of include the following.
U.S. Pat. No. 4,569,820 discloses stackable fuel elements machined from graphite and having fuel chambers that receive nuclear fuel in the form of coated particles. Coolant holes are machined through the graphite blocks separate from the fuel chambers so that the coolant does not directly contact the fuel.
U.S. Pat. No. 4,759,911 discloses a gas cooled nuclear fuel element formed from a plurality of progressively sized rigid porous cylinders nested together that have varying quantities of nuclear fuel deposited thereon.
U.S. Pat. No. 3,560,339 discloses a nuclear reactor fuel element having an elongated tubular cladding which contains fuel particles and a plurality of discs smaller in diameter than the internal diameter of the cladding.
U.S. Pat. No. 4,704,248 discloses a nuclear fuel element formed from an elongate block of refractory material having a plurality of separate coolant passages and elongate fuel holes. End seals insure proper coolant flow through the coolant passages.
U.S. Pat. No. 3,873,420 discloses a fuel element assembly comprising a prismatic block having fuel containing bores and interstitial coolant conducting bores extending end-to-end. The fuel comprises stacks of annular compacts that line the fuel containing bores and define central coolant flow channels through the fuel. The block provides support to the annular compacts.
U.S. Pat. Nos. 3,891,502, 3,988,397, and 4,017,567 disclose block fuel elements formed from graphite matrix.
Although the above patents disclose a variety of fuel elements, the solid blocks disclosed all provide for separate coolant channels and fuel-containing channels whereby heat generated by the fuel is removed from the blocks and the coolant does not have direct contact with the fuel itself. This results in increased fuel element, core, and reactor size. There exists a need for gas cooled fuel elements that are smaller in size than current fuel elements but are capable of producing the same amount of power.